The invention relates to a motor vehicle outer tank for a cryogenic fuel which is situated in an inner tank which is positioned within the outer tank.
An outer tank for a known cryogenic fuel is known for example from U.S. Pat. No. 6,347,719 B1. Said known outer tank is of a lightweight design for stratospheric missiles. Said outer tank is of spherical design and is formed by a sandwich wall. Provided spaced apart from said sandwich wall is a likewise spherical wall, composed of metal, as an inner tank. The inner wall and the sandwich outer wall are connected to one another by means of welding, specifically at two opposite meridians of the container, which results in a composite design, that is to say the outer tank is not self-supporting. An outer tank of said type is voluminous as a result of its spherical design and can be installed in a motor vehicle only with difficulty and with a large loss in useful space. A further disadvantage of said known outer tank is to be considered that of production being complex, especially since the outer and inner tanks can only be produced together, and the individual parts are highly fragile before being joined together.
DE 101 63 029 A1 discloses a high-pressure hydrogen tank in which an inner polyethylene lining is surrounded by an outer winding which is intended to prevent a bulging effect. The inner side of the lining is also provided with a hydrogen barrier layer. A tank of said type likewise entails space problems, in particular in motor vehicle construction.
Conventional reinforcement measures for buckling-critical containers with large surfaces are usually very massive; thick sheet metal wall thicknesses result in both complex production techniques and also joining techniques as a result of the use of a large number of web sheets or bulkhead sheets in cryogenic inner tanks, and the ultimate result is a high weight. Said inner tank reinforcement measures, in order to counteract the buckling of the outer tank caused by the atmospheric pressure, with welded-in web sheets can never be used for cryogenic outer tank containers because this does not permit the inner tank mounting and because more layers for inner tank insulation must be positioned between the inner and outer tanks and there is therefore no space for inner reinforcements of said type. In addition, there may be no heat bridges between the outer tank and the inner tank.